Son Doong Cave (Vietnamese: Hang Son Doong) is world's largest cave, located in the heart of Phong Nha Ke-Bang National Park, Vietnam. It was first discovered in 1990, by a local man named Ho Khanh but he returned home and forgot about the cave. In 2008, he found the cave again and took note of the path, and subsequently led Howard and Deb Limbert of the British Cave Association to the cave for the first expedition. The first expedition was halted by a 90m high calcite barrier, which was jokingly dubbed the “Great Wall of Vietnam.” It wasn’t until the second expedition in 2010, when the Great Wall was finally climbed and the end of the cave was found. The main huge passage is over 5km long with sections reaching up to 200m tall and 150m wide.
The name "Son Doong" cave means "mountain river cave” was created 2.5 million years ago by river water eroding away the limestone underneath the mountain. The cave is unique for the two enormous dolines and underground rainforests. Where the limestone was weak, the large dolines (or skylights) collapsed sometime in the last 500,000 years, creating massive openings to the outside world and this has allowed foliage to grow inside the cave. The ecosystem created within the cave has its own weather system and creates its own clouds.
It also features various unusual cave formations, including huge cave pearls, towering stalagmites, phytokarst and fossils dating back millions of years. Cave pearls the size of baseballs and stalagmites the size of tall buildings (hanging at 80 meters tall) have formed from water dripping from the cave ceiling. In 2013, the cave was opened to the public. To reach Hang Son Doong, you need to pass through the only village located inside the Phong Nha Ke-Bang National Park. The Ban Doong ethnic minority village is only accessible by foot, as it is surrounded by dense jungles.